you can fly from one place to another, and watch any place on this Earth without ever leaving your cave. You tell him you never have to run after your food, or fear that you run out of it. Your ancestor will have a hard time believing you. In his world only his gods can do all that.
Then you tell him how some of your friends think his way of life is preferable for health, which is why you are visiting him because you want to see for yourself. Before I get to your ancestor's most likely answer, let's get on the same page with those friends of ours first.
You have probably heard them talk about the past 10,000 years having done nothing to our genetic make-up. In other words, your ancestor's DNA blueprint was the same as yours. Today this blueprint collides with a space age environment in which we don't expend any energy to get our food, and the food we acquire delivers far more energy and far less nutrients than what had been the case during 99.9% of human evolution.
According to this view, today's epidemics of obesity, diabetes, cardiovascular diseases and cancer are simply the collateral damage of this collision. This explanation is so persuasive that it is being parroted by every media type and talking head who can spell the word 'genetics'. I'm afraid it is not that simple. Here is why:
Remember when the 3 billion letters, or base-pairs, of the human genome had first been decoded at the beginning of this century. This decryption had been delivered with the promise of revolutionizing medicine. Aside from new therapies, the hottest items were prognostic and diagnostic tools, which, we were made to believe, would lay in front of each individual his biomedical future. And with this ability to predict would come the ability to prevent, specifically all those diseases which result from an unfavorable interaction between genes and environment.
Almost ten years later we are nowhere near this goal. OK, we have identified some associations between some genetic variants and the propensity to become obese or get a heart attack or diabetes. But these associations are far from strong and they hardly help us to improve risk prediction. Just this year, Vaarhorst and colleagues had investigated the ability of a genetic risk score to improve the risk prediction of conventional risk scores which are based on biomarkers, such as the ones used in the Framingham score. Less than 3% of the study participants would have been reclassified based on the genetic risk score [1].
In a study which was released just yesterday, genetic markers for the development of diabetes in asymptomatic people at high risk, did not improve conventional biomarker risk scoring at all [2].
In a study which was released just yesterday, genetic markers for the development of diabetes in asymptomatic people at high risk, did not improve conventional biomarker risk scoring at all [2].
Obviously we are not simply our genes. This is because genes do not make us sick or healthy. Genes make proteins. And on the way from gene to protein a lot of things happen on which genes do not have any influence. To express a gene, as biologists call it, that gene must first be transcribed on RNA and then translated from RNA into the final protein. Whether a gene is transcribed in the first place depends on whether it is being made accessible for this transcription process. Today we know at least two processes which can "silence" the expression of a gene, even though it is present in your DNA. These processes are called DNA methylation and histone modification. Simply imagine them as Mother Nature's way of keeping a gene under wraps.
That's a good thing if the protein product of the silenced gene would be detrimental to your health. It could well be the other way round, too. Anyway, these happenings have been called epigenetics. Epigenetic mechanisms enable cells to quickly match their protein production with changing environmental conditions. No need to wait for modifications of the genetic blueprint which takes many generations and a fair element of chance to materialize. The most astonishing discovery is that these epigenetic changes may become heritable, too. Which means, there is really no need to change the genetic code.
I believe you get the picture now. While it is true that your ancestor's genetic code is indistinguishable from yours 10,000 years later, the way your body expresses this code in the form of proteins and hormones can differ in many ways. Which is why researchers are now as much excited about epigenetics as they used to be about genetics 10 years ago.
I don't want to be the party pooper, but whenever I see such excitement I'm reminded of how it has often evaporated after some further discoveries. Here I'm skeptical because of the picture, which we are beginning to see. Insulin, for example, is known to regulate the expression of many genes. At least in rats it has been shown that insulin's suppressive effect on gene expression in the liver, can be altered by short term fasting [3]. That means, relatively minor behavioral changes may affect the way our organism expresses its genetic code.
Observations like these support the idea that we are not our genes, but what we make of them. In plain words: let's not hide behind the "it's-our-stone-age-genes" excuse, to explain why we are fat and lazy and ultimately chronically sick.
Now, back to your ancestor and his response to your friends' suggestions that his way of life is preferable for health. When you also tell him you live a lot longer than the 40 years he has on average, he'll tell you: You have got some nutcase friends over there. Let me live like a god first and then I'll worry about health later.
Maybe, we are not so different from our stone age ancestors after all. Lu, Y., Feskens, E., Boer, J., Imholz, S., Verschuren, W., Wijmenga, C., Vaarhorst, A., Slagboom, E., Müller, M., & Dollé, M. (2010). Exploring genetic determinants of plasma total cholesterol levels and their predictive value in a longitudinal study Atherosclerosis, 213 (1), 200-205 DOI: 10.1016/j.atherosclerosis.2010.08.053
Zhang Y, Chen W, Li R, Li Y, Ge Y, & Chen G (2011). Insulin-regulated Srebp-1c and Pck1 mRNA expression in primary hepatocytes from zucker fatty but not lean rats is affected by feeding conditions. PloS one, 6 (6) PMID: 21731709
